Thailand announced its first case of Middle East Respiratory Syndrome, or MERS, on Friday after a 75-year-old businessman from Oman was diagnosed at a hospital near Bangkok.

According to Reuters, the unnamed man first arrived in the Southeast Asian nation on Monday to seek medical treatment for a heart problem at a private hospital.

Thai Health Ministry officials said it took them four days to verify the case, raising concerns that the deadly virus may have spread in the interim, Reuters reports.

A total of 59 people are being monitored for symptoms after coming into contact with the infected man, who is now being held in quarantine at an infectious-disease clinic. Thai Public Health Minister Rajata Rajatanavin told Reuters that three of those under observation have already been hospitalized.

The announcement comes as South Korea’s MERS outbreak appears to be stabilizing. Twenty-four people have died from the virus in the East Asian country, while a total 166 people have been infected.

Thai businesses have already been affected by the latest case, according to Reuters, with shares in the operator Airports of Thailand dropping 4.2% to their lowest value in three weeks.